The present invention relates to a light source for a photographic printer and, more particularly, to a printer light source which is designed so that the light source efficiency in a photographic printer is improved, thereby enabling the light intensity to be increased.
As shown in the perspective view of FIG. 5, a conventional photographic printer (hereinafter referred to simply as "printer") uses a diffuser D as a direct light source for illuminating a film F to be printed off, although the actual light source is a lamp S. Light from the lamp S is diffused by a diffusing box M and the diffuser D, thereby producing diffused light that is required as a printer light source. Thus, blemishes and dust which may be present on an image recorded on the film F are made inconspicuous, and unevenness of printing is eliminated. In addition, it is necessary to produce light which is directed in a direction different from the optical axis of printing light for purposes other than the printing purpose, i.e., measurement of light transmitted by the film F, transmission of light to a scanner, or visual observation. The diffuser D is also used for these purposes.
The present applicant has proposed various diffuser structures: a diffuser that anisotropically diffuses light in a direction perpendicular to the longitudinal direction of the film F (Japanese Patent Application Laid-Open (KOKAI) No. 01-298337); another diffuser that has minute steeple-shaped projections (Japanese Patent Application Laid-Open (KOKAI) No. 02-278243); and so forth.
Incidentally, if there is dust or a blemish on the surface of the diffuser D, the film F and the diffuser D must be spaced apart from each other by 10 mm or more so that the image of the dust or blemish will not be projected on the print. However, as the distance between the film F and the diffuser D increases, the quantity of light entering the printing lens L decreases, resulting in a reduction of the light source efficiency.
On the other hand, the distance between the film F and the diffuser D may be made shorter than 10 mm, provided that the depth of focus of the printing lens L is made satisfactorily shallow. If the distance is shortened in this way, however, a focusing failure is likely to occur because of minute curl of the film F. Therefore, it is impractical to shorten the distance between the film F and the diffuser D as described above.
Thus, in the conventional diffusion light sources for printers, a certain distance must be ensured between the film and the diffuser. Therefore, only a part of light energy emitted from the diffusing device can be used for printing, disadvantageously.